From phase partitioning to corrosion resistance: Opposite effects of γ' and σ stabilizers in chloride-induced hot corrosion

The role of phase partitioning in governing chloride-induced hot corrosion remains poorly understood, despite its critical importance for the design of corrosion-resistant high-temperature coatings. In this work, Mo and Ta were selected as representative σ- and γ′-stabilizing elements, respectively, to investigate how phase-partitioning behavior influences corrosion resistance in NaCl-containing environments. A series of Cr-substituted MCrAlY coatings were prepared and exposed to NaCl‑induced hot corrosion at 750 °C. The results reveal two fundamentally different degradation pathways. Mo progressively partitions into the σ phase, promoting the formation of a protective multilayered oxide architecture that suppresses chlorine ingress and mitigates scale failure. In contrast, Ta remains preferentially dissolved in the γ′ phase and subsequently forms Ta-rich oxides with large volume expansion, leading to crack initiation, localized internal oxidation, and accelerated degradation. Time-resolved XRD analysis combined with Density Fictional Theory calculations confirm the opposite partitioning tendencies of Mo and Ta and reveals their distinct site-occupancy preferences in σ and γ’ phases. This study a direct link between phase partitioning and corrosion resistance and demonstrate that the corrosion behavior of chloride-exposed coatings is governed not only by alloy chemistry but also by the phase-selective distribution of alloying elements. The proposed phase-partitioning framework provides new guidance for the design of corrosion-resistant MCrAlY coatings for marine environments.